/*
 * Copyright (C) 2009 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.primitives;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import java.util.Comparator;

/**
 * Static utility methods pertaining to {@code byte} primitives that interpret
 * values as <i>unsigned</i> (that is, any negative value {@code b} is treated
 * as the positive value {@code 256 + b}). The corresponding methods that treat
 * the values as signed are found in {@link SignedBytes}, and the methods for
 * which signedness is not an issue are in {@link Bytes}.
 * 
 * @author Kevin Bourrillion
 * @since 2009.09.15 <b>tentative</b>
 */
public final class UnsignedBytes {
    private UnsignedBytes() {
    }

    /**
     * Returns the {@code byte} value that, when treated as unsigned, is equal
     * to {@code value}, if possible.
     * 
     * @param value
     *            a value between 0 and 255 inclusive
     * @return the {@code byte} value that, when treated as unsigned, equals
     *         {@code value}
     * @throws IllegalArgumentException
     *             if {@code value} is negative or greater than 255
     */
    public static byte checkedCast(long value) {
        checkArgument(value >> 8 == 0, "out of range: %s", value);
        return (byte) value;
    }

    /**
     * Returns the {@code byte} value that, when treated as unsigned, is nearest
     * in value to {@code value}.
     * 
     * @param value
     *            any {@code long} value
     * @return {@code (byte) 255} if {@code value >= 255}, {@code (byte) 0} if
     *         {@code value <= 0}, and {@code value} cast to {@code byte}
     *         otherwise
     */
    public static byte saturatedCast(long value) {
        if (value > 255) {
            return (byte) 255; // -1
        }
        if (value < 0) {
            return (byte) 0;
        }
        return (byte) value;
    }

    /**
     * Compares the two specified {@code byte} values, treating them as unsigned
     * values between 0 and 255 inclusive. For example, {@code (byte) -127} is
     * considered greater than {@code (byte) 127} because it is seen as having
     * the value of positive {@code 129}.
     * 
     * @param a
     *            the first {@code byte} to compare
     * @param b
     *            the second {@code byte} to compare
     * @return a negative value if {@code a} is less than {@code b}; a positive
     *         value if {@code a} is greater than {@code b}; or zero if they are
     *         equal
     */
    public static int compare(byte a, byte b) {
        return (a & 0xFF) - (b & 0xFF);
    }

    /**
     * Returns the least value present in {@code array}.
     * 
     * @param array
     *            a <i>nonempty</i> array of {@code byte} values
     * @return the value present in {@code array} that is less than or equal to
     *         every other value in the array
     * @throws IllegalArgumentException
     *             if {@code array} is empty
     */
    public static byte min(byte... array) {
        checkArgument(array.length > 0);
        int min = array[0] & 0xFF;
        for (int i = 1; i < array.length; i++) {
            int next = array[i] & 0xFF;
            if (next < min) {
                min = next;
            }
        }
        return (byte) min;
    }

    /**
     * Returns the greatest value present in {@code array}.
     * 
     * @param array
     *            a <i>nonempty</i> array of {@code byte} values
     * @return the value present in {@code array} that is greater than or equal
     *         to every other value in the array
     * @throws IllegalArgumentException
     *             if {@code array} is empty
     */
    public static byte max(byte... array) {
        checkArgument(array.length > 0);
        int max = array[0] & 0xFF;
        for (int i = 1; i < array.length; i++) {
            int next = array[i] & 0xFF;
            if (next > max) {
                max = next;
            }
        }
        return (byte) max;
    }

    /**
     * Returns a string containing the supplied {@code byte} values separated by
     * {@code separator}. For example, {@code join(":", (byte) 1, (byte) 2,
     * (byte) 255)} returns the string {@code "1:2:255"}.
     * 
     * @param separator
     *            the text that should appear between consecutive values in the
     *            resulting string (but not at the start or end)
     * @param array
     *            an array of {@code byte} values, possibly empty
     */
    public static String join(String separator, byte... array) {
        checkNotNull(separator);
        if (array.length == 0) {
            return "";
        }

        // For pre-sizing a builder, just get the right order of magnitude
        StringBuilder builder = new StringBuilder(array.length * 5);
        builder.append(array[0] & 0xFF);
        for (int i = 1; i < array.length; i++) {
            builder.append(separator).append(array[i] & 0xFF);
        }
        return builder.toString();
    }

    /**
     * Returns a comparator that compares two {@code byte} arrays
     * lexicographically. That is, it compares, using
     * {@link #compare(byte, byte)}), the first pair of values that follow any
     * common prefix, or when one array is a prefix of the other, treats the
     * shorter array as the lesser. For example,
     * {@code [] < [0x01] < [0x01, 0x7F] <
     * [0x01, 0x80] < [0x02]}. Values are treated as unsigned.
     * 
     * <p>
     * The returned comparator is inconsistent with
     * {@link Object#equals(Object)} (since arrays support only identity
     * equality), but it is consistent with
     * {@link java.util.Arrays#equals(byte[], byte[])}.
     * 
     * @see <a href="http://en.wikipedia.org/wiki/Lexicographical_order">
     *      Lexicographical order</a> article at Wikipedia
     * @since 2010.01.04 <b>tentative</b>
     */
    public static Comparator<byte[]> lexicographicalComparator() {
        return LexicographicalComparator.INSTANCE;
    }

    private enum LexicographicalComparator implements Comparator<byte[]> {
        INSTANCE;

        public int compare(byte[] left, byte[] right) {
            int minLength = Math.min(left.length, right.length);
            for (int i = 0; i < minLength; i++) {
                int result = UnsignedBytes.compare(left[i], right[i]);
                if (result != 0) {
                    return result;
                }
            }
            return left.length - right.length;
        }
    }
}
